The Christmas Invasion was the first episode of Doctor Who to premiere on Christmas Day since "The Feast of Steven", the seventh part of the 1966 epic twelve-part serial The Daleks' Master Plan. However, unlike that episode, The Christmas Invasion was specially commissioned by BBC One to be transmitted outside the programme's normal broadcasting season. It was thus the first in the modern tradition of the "Christmas special", and its sixty-minute running time made it then the longest episode yet produced by BBC Wales.

More importantly, it was the first full story to feature the Tenth Doctor, played by David Tennant. Its initial pre-titles sequence on the Powell Estate was later used to "bookend" the closing scenes of The End of Time. Its setting was the first and last place on Earth the Tenth Doctor saw.

It is Christmas Eve on Earth. As Jackie prepares presents and Mickey works in the garage, both of them hear the distinctive sound of the TARDIS' engines. Rushing out into the street of the Powell Estate, they see the TARDIS blink into existence above them, ricochet off a few buildings and a post van, then come to a crashing halt. A strange man stumbles out of the police box doors, greets them by name and wishes them a merry Christmas before collapsing. Rose follows and, in response to Jackie and Mickey's questions, identifies the stranger as the Doctor.

They bring the Doctor to Jackie's flat and dress him in pyjamas belonging to Howard, Jackie's current beau, who has the habit of keeping pieces of fruit in his pocket for snacks. While Rose discusses the Doctor's change of appearance and the fact he has two hearts with Jackie, they do not see a wisp of vortex energy emerging from the Doctor's mouth, which then floats into space. On television, Prime MinisterHarriet Jones and project director Daniel Llewellyn give a press conference about the Guinevere One space probe, which is about to land on Mars. In space, however, the probe is swallowed up by an island-like spaceship.

That evening, Rose and Mickey go Christmas shopping, but are attacked by a group of masked Santas armed with lethal musical instruments. Managing to escape when the tuba mortar brings a giant Christmas tree down on the Santas, Rose realises that the Santas must be after the Doctor. She and Mickey rush home. When they reach the flat, Rose notices an unfamiliar Christmas tree in the sitting room, which Jackie says was delivered to the door. As they realise that none of them purchased the tree, it comes to life, whirling around with razor-sharp branches.

The three retreat to the bedroom, the "Christmas tree" in hot pursuit. Rose places the sonic screwdriver in the still-comatose Doctor's hand and asks him to help her. Reacting instinctively, the Doctor rises as the tree bursts through the door and disintegrates the tree with the screwdriver. He then strides outside the flat to see who was remotely controlling the tree. From ground level, the Santas stare up at the Doctor, but transmat away when the Doctor points the sonic screwdriver at them. The Doctor calls them "pilot fish" and collapses in pain, saying that Rose woke him up too soon: he is still regenerating. The energy leaking from him has attracted attention, and if the “pilot fish” could trace it, then something bigger is coming. He then loses consciousness again.

PM Harriet Jones during the Sycorax crisis.

The first signal from Guinevere One arrives: a distinctly alien face, which is soon broadcast all over the world. Llewellyn is escorted by Major Blake to the Tower of London, which houses a facility run by the United Nations Intelligence Taskforce. There, he meets the Prime Minister and her aide, Alex, who tells him that the cover story is that a student in a mask hacked into the television signal. Llewellyn is shaken to realise that extraterrestrial life does exist, and that both the British government and the United Nations are aware of this. A technician, Sally Jacobs, explains that the signal did not come from Mars but 5000 miles above the planet's surface, which means that there is a ship, and it is moving rapidly towards Earth.

As Rose and Mickey use his laptop to monitor UNIT's readings, the aliens send another signal. The aliens speak in their own language, but Rose does not understand it. Normally, the TARDIS would translate it for her, but it seems that with the Doctor unconscious, that function is not working.

At UNIT, Blake orders the use of translation software. With no sign of the Doctor, Jones asks Blake about "Torchwood". She knows that she is not supposed to know about them – not even the United Nations knows — but she wants them to be ready.

The software rather imprecisely translates the message. The aliens are the Sycorax, and they are claiming the planet as their own, demanding surrender or "they" will die. Their word for "human" also appears to be similar to that of "cattle", temporarily baffling UNIT. Jones declines to surrender, warning the Sycorax that the planet is armed. As dawn rises over London, the Sycorax respond. With a wave of the leader's hand, blue energy sweeps over a third of the world's population, mesmerising them. The mind-controlled people, Sally Jacobs amongst them, climb to the highest spots they can find (primarily the roofs of buildings), and stand at the edge, poised to jump.

Checking the UNIT staff's medical records, Llewellyn discovers that all the affected people have A+ blood. The Sycorax found the sample of A+ blood that was sent with other materials on Guinevere One to identify the human race in case of alien contact, and are somehow using that as a control mechanism. Desperate now, Jones gives an emergency broadcast on television, pleading for the Doctor's help if he is out there. She also informs the public that the Queen's Christmas speech has been cancelled and finds that the Royal Family are "on the roof".

Harriet Jones aboard the Sycorax's ship

Just then, the shockwave of the Sycorax ship entering the atmosphere shatters windows all over the city; the gigantic craft takes position above the centre of London as the frightened population watch. Rose, driven to despair by the Doctor's comatose state and not knowing what else to do, asks Mickey and Jackie to help move the Doctor to the safety of the TARDIS. Jackie gathers food and other supplies, including a thermos flask of tea.

The Sycorax transmat Jones, Alex, Blake and Llewellyn up to their ship. The Sycorax leader removes his helmet, revealing a skinless face surrounded by a mantle of bone. His hand hovering over a large glowing button, he demands immediate surrender, or he will order the controlled humans to jump. Llewellyn tries to reason with the Sycorax, but is reduced to a pile of bones by the leader's energy whip, as is Blake when he protests. Half of the world will be sold into slavery or a third will die; it is Jones's choice.

As Rose and Mickey move the Doctor into the console room, Jackie goes back to get more supplies. Rose, having apparently given up, broods by the console as Mickey tries to use the TARDIS scanner to tune into what is happening, but the time machine's advanced technology is detected by the Sycorax. Outside, Jackie watches helplessly as the TARDIS is transmatted up. Not realising that they are aboard the Sycorax ship, Rose steps out of the TARDIS, and screams when she sees the aliens. Mickey rushes out after her, dropping the flask of tea, which spills and starts dripping through the grilles at the base of the console next to the Doctor's unconscious form. The Doctor breathes in the fumes created as the tea sparks against various components.

Rose tries to bluff the Sycorax by quoting various things and races she has encountered on her travels, commanding them to leave, but is answered with laughter. The Sycorax leader taunts her attempts to pass off second-hand knowledge as authority, but as he gloats, his alien words start turning into English. Rose realises that the TARDIS translation is working again, and as the Doctor must be conscious for it to be active, that can mean only one thing: the Doctor is awake. On cue, the doors of the police box open and the Doctor stands there, smiling as he says, "Did you miss me?"

Easily deactivating the Sycorax leader's energy whip and breaking his staff, the Doctor bluntly tells the alien to wait while he gets more important things out of the way, namely, getting reacquainted with his friends. Disappointed at not being "ginger" (red haired), and somewhat annoyed at Rose's speed in giving up on him, he tells them that all he needed was a "good cup of tea; a superheated infusion of free radicals and tannin. Just the thing for healing the synapses." As the Sycorax leader demands to know who he is, the Doctor blithely strides across the ship's floor, nattering on cheerfully and still working out what his personality is like in this new incarnation. He walks up to the glowing button, discovers that it is powered by A-positive human blood, and quickly deduces that the Sycorax are using blood control — they're controlling all the humans with A-positive blood. The Doctor tells the leader that in his unstable state, when he sees a large glowing button he just cannot help himself — and to everyone's shock, he pushes it.

The Doctor Quotes the Lion King - Doctor Who - The Christmas Invasion - BBC

The Doctor accidentally quotes The Lion King.

However, instead of sending the possessed crowds on Earth to their deaths, it simply releases them from the Sycorax control. The Doctor explains that blood control is like hypnosis: you cannot hypnotise a person and convince them to kill themselves as the survival instinct is too strong. The Sycorax were bluffing, and the Doctor merely called them on it. The leader says that they can still conquer Earth with an armada, but the Doctor demands that the humans be left alone (quoting part of "The Circle of Life" from The Lion King in the process), ultimately challenging the leader to single combat for the planet.

The swordfight goes from inside the ship to its exterior. In the midst of it, the leader cuts the Doctor's hand off. However, the Doctor is still in the first 15 hours of his regeneration cycle, and regrows his hand. He gains an advantage over the Sycorax leader and triumphs. Holding the leader at sword point at the ship's edge, the Doctor extracts an oath from the leader to leave the planet and never return, in return for the Doctor sparing his life. As the Doctor walks back, celebrating his victory with Rose, the leader tries a final attack whilst the Doctor's back is turned. The Doctor calmly bounces a satsuma he finds in Howard's dressing gown off a control button, opening a section of the ship's wing beneath the leader, sending the alien plunging to his death. The new Doctor is not a man willing to grant second chances.

The Doctor sends the other Sycorax on their way with a reminder that the planet Earth is defended. They are transmatted back to London, and Jones asks if there are more aliens out there. The Doctor notes that there are thousands; the human race is being noticed more and more. As Jones ponders this, visibly troubled, Alex receives a telephone call and quietly informs Jones that Torchwood is ready. Jones seems reluctant, but nevertheless gives the order to fire. Five green beams converge as one over London, and the resulting energy burst destroys the Sycorax ship as it heads into space.

The Doctor glares at Jones, furious, but she tries to justify the use of the weapon (engineered from a crashed spaceship ten years previously) as defending the planet, especially since the Doctor cannot be there all the time. The Doctor bitterly says he should have warned the Sycorax to run, as the real monsters, the humans, are coming. When Jones asks if she should consider the Doctor another alien enemy, the Doctor warns her that he can bring down her government with just six words. He whispers them in Alex's ear: "Don't you think she looks tired?"

Jackie, Mickey and Rose serve Christmas dinner in the flat. The Doctor looks through the TARDIS wardrobe, finally settling on a brown pinstripe suit and a long brown coat. He joins the others for dinner, and they watch Harriet Jones on the television, fending off rumours about her ill-health and a pending vote of no confidence in the House of Commons. Outside, what looks like snow is falling over London, accompanied by shooting stars, but the Doctor points out that it is, in fact, ash — the remains of the Sycorax spaceship. It is a new start for Earth, however; with so many people seeing the Sycorax ship, there is no covering up the existence of aliens this time.

But there are new worlds to see and explore. With a now-trusting Rose by his side and eager to continue their travels, the Doctor looks up into the sky to choose a star for their next destination, assuring her that it will be, in the words of his previous incarnation, "fantastic".

Not every person who worked on this adventure was credited. The absence of a credit for a position doesn't necessarily mean the job wasn't required. The information above is based solely on observations of the actual end credits of the episodes as broadcast, and does not relay information from IMDB or other sources.

With The Christmas Invasion came an explosion in the number of people regularly credited on Doctor Who. In particular, the art department got much more specific crediting than had ever been the case in series 1. This trend of expanding the number of art department personnel credited would continue right through to series 5, with each series regularly crediting a few more positions.

This story was effectively the first since 1989's Survival to credit the role as "The Doctor".

The "middle eight" section of the theme tune is restored in this episode and is heard for the first time in the revived series.

Before this episode was broadcast, a fictional tie-in website for the Guinevere One project was created and launched by the BBC. The site includes an introduction by Harriet Jones and an interview with the project director, ProfessorDaniel Llewellyn. The site claims that the probe was developed by the British Rocket Group. The organisation's logo partially appears in this episode, in the televised press conference with Professor Llewellyn. The name of the organisation was first mentioned in Remembrance of the Daleks and is a reference to the British Experimental Rocket Group from the Quatermass science fiction serials of the 1950s. David Tennant had previously starred in the 2005 BBC live remake of The Quatermass Experiment as Doctor Gordon Briscoe, and Quatermass' first line to Briscoe was changed by actor Jason Flemyng during the broadcast from "Good to have you back, Gordon" to "Good to have you back, Doctor" — Tennant's casting as the Doctor was announced two weeks after Quatermass went to air, and his castmates would have been aware of the speculation during rehearsals.

Just before the opening credits sequence, Jackie says the line, "Doctor? Doctor who?", continuing a long-running in-joke. Unlike many instances of the joke, however, the line primarily plays as a genuine question, since she has never before met the Tenth Doctor and knows nothing of regeneration.

The Tenth Doctor speaks with an accent similar to Rose's but unlike the Ninth Doctor's Northern one. In a radio interview broadcast on 23 December 2005, Tennant explained that a line of dialogue had been scripted for this episode which explained that the newly regenerated Doctor had imprinted on Rose's accent, "like a chick hatching from an egg", but the line was deleted from the final episode.

The opening shot of this episode, in which the Earth and its moon appear, is reused footage from the opening shot of the episode Rose.

According to press reports[source needed] released before this episode was broadcast, producer Russell T Davies stated that he believed Christmas specials should include traditional Christmas items such as sleigh bells, snow, reindeer, and Santa.

Another song featured in this episode is "Song for Ten", an original composition by Murray Gold sung by Tim Phillips. The next two Christmas specials included an original song on the soundtrack. The Phillips version of the song was very brief, and when the time came to compile a soundtrack album, new lyrics were written for the song (reflecting the events of Doomsday) and it was recorded by Neil Hannon. "Song for Ten" is the first original song commissioned for Doctor Who since the untitled rap song for the Ringmaster heard during the 1988 story The Greatest Show in the Galaxy.

One of the outfits considered by the Doctor in the wardrobe is the costume worn by David Tennant in his previous role as Casanova in the eponymous television serial.

When the Doctor is leaving the wardrobe near the end of the episode, a long coat and long yellow and red scarf (possibly Tom Baker's famous scarf) can be seen hanging from the very hat rack that appeared in the TARDIS in the Tom Baker years.

This marks the first time in the new series that any room in the TARDIS other than the console room is seen on-screen.

In a scene filmed for the episode, but deleted before broadcast (though included on the DVD), the Doctor attempts to utter his predecessor's catchphrase, "Fantastic!" but due to his "new teeth" (ref. his comments at the end of The Parting of the Ways) finds it initially impossible to do so. This scene was intended to set up the final scene of the episode in which the new Doctor finally utters the word, "Fantastic!"

The Christmas Invasion can be viewed in its entirety on the BBC America website.

A signal intrusion incident that occurred in Chicago during an airing of the Fourth Doctor serial Horror of Fang Rock is referenced by Harriet Jones' aide Alex when he says the official story of the Sycorax appearing via the probe is because of "a mask, some sort of prosthetic. Students hijacking the signal."

After the announcement that Christopher Eccleston would leave after the first series, there were erroneous reports that the regeneration was to take place during the Christmas special, not during The Parting of the Ways. (This may have been an intentional red herring in order to maintain at least some element of surprise for the series finale given that the BBC had accidentally blown Russell T Davies' plan for a surprise regeneration.)

Harriet Jones's decision to destroy the Sycorax spaceship, despite the fact it was leaving Earth, echoes Margaret Thatcher's decision to sink the Argentinian ship Belgrano in the 1982 Falklands War, even though evidence suggests it was actually leaving British waters.

Guinevere One, the name of the probe that Earth sends to Mars, references the myths of King Arthur. In those stories, Guinevere was Arthur's Queen Consort. Her name is an old French form of the Welsh name Gwenhwyfar, which can be translated as "white shadow". Her adulterous affair with Arthur's chief knight, Lancelot, and betrayal of her husband lead to the downfall of their kingdom. When the Seventh Doctor was recognised as Merlin, Arthur's advisor, he assumed that he would later find himself in this role. (TV: Battlefield)

When Mickey calls Rose to check out the military broadcast of the Sycorax ship, you can see for a split-second the video player playing the broadcast, revealing that it was not green-screened, but a video playing on the computer.

Although it has been a very short time since the Doctor regenerated, as Rose passes the door of the TARDIS after the Doctor collapses, her hair is visibly longer. (TV: The Parting of the Ways) This exposes the several month break between the wrapping up of Series 1 production and the start of Series 2 production, during which time Billie Piper allowed her hair to grow longer.

When proclaiming his new form to be "lucky", the Doctor is facing towards the Sycorax ship, but when mentioning being in the first 15 hours of his regenerative cycle, he is facing away from the Sycorax ship. He is facing the ship again when his hand regrows.

Jones's destruction of the Sycorax ship and the Doctor's angry reaction are similar to the Brigadier using explosives to seal off the Silurian hibernation chambers even as the Doctor departs to begin peace negotiations. (TV: Doctor Who and the Silurians)

Harriet Jones introduces herself regularly as "Harriet Jones, Prime Minister" to which the common reply is, "Yes, I know who you are"; she did the same before becoming Prime Minister, introducing herself to everyone as "Harriet Jones, MP for Flydale North". (TV: Aliens of London, World War Three)

She would later continue this as former Prime Minister, with a similar response. (TV: The Stolen Earth)

The group met Professor Yana, who Martha noticed had a fob watch. After her experience with the chameleon arch, she thought Yana was a benevolent Time Lord that became human, but Yana's true identity belonged to the Master, who had fled the Time War. After regenerating, he stole the Doctor's TARDIS and fled the planet, but the Doctor tampered with his TARDIS to trap him on Earth. (TV: Human Nature, Utopia)

During the Master's confrontation with Lord PresidentRassilon, Wilfred Mott rescued a trapped worker in the Gate's radiation booth and took his place. The booth's anti-leak security measures only allowed one person to exit while another person had to be locked inside. (TV: The End of Time)

The Doctor cut the link holding Gallifrey out of the Time War, which sent the Time Lords back into the battlefield, the Master joining them. However, he left the Immortality Gate's nuclear bolt running. It went into meltdown and the excess radiation would have dumped into the containment booth with Wilf still inside. Trying to operate the booth in any way would also have the same result. In order to rescue Wilf, the Doctor had to enter the booth and expose himself to the radiation, leading to his regeneration. (TV: The End of Time)